(1) Field of the Invention
This invention relates to web-indexing apparatus for use, for example, in label overprinting machines.
(2) Summary of the Prior Art
The requirement to index a web intermittently is encountered in many machines one example being self-adhesive label overprinting machines in which it is necessary to advance the web through the machine at the instant of printing by a rotary type drum. In previous proposals, in such machines the indexing of the web has been effected by purely mechanical means but such previous machines have the disadvantage that it is necessary to set-up mechanically a machine for any given run of labels on a web and this can be time-consuming and, moreover, the accuracy is not always as high as is desirable, with the result that registration is lost over a long run of labels.
As printing speeds increase and hence the velocity of the web of labels through the machine, it becomes even more essential accurately to synchronise the arrival of a given label at the printing station than in relatively low speed machines hitherto used.